Transcript Human Physiology

Chapter 8
The Central
Nervous
System
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CNS
 Consists
of brain and
spinal cord
 Receives input from
sensory neurons
 Directs activity of motor
neurons
 Association neurons
integrate sensory and
motor activity
 Perform learning and
memory
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CNS continued
CNS
composed of gray and white matter
Gray matter consists of neuron bodies and dendrites
White matter (myelin) consists of axon tracts
Adult brain weighs 1.5kg
Contains 100 billion neurons
Receives 20% of blood flow to body
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Embryonic Development
tube forms from groove in ectoderm by 20th day
 Becomes the CNS
 Neural crest cells develop where tube fuses
 Become ganglia of PNS
 Neural
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Embryonic Development continued
 During 5th
week: Forebrain elaborates into telencephalon and
diencephalon
 Midbrain does not subdivide
 Hindbrain forms metencephalon and myelencephalon
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Cerebrum
Is
largest part of
brain (80% of
mass)
Is responsible for
higher mental
functions
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Cerebral Cortex continued
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Electroencephalogram (EEG)
Measures
electrical activity of cerebral cortex
Used to diagnose epilepsy and brain death
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EEG Waves
Alpha
waves are recorded
from parietal and occipital
lobes with person awake,
relaxed, eyes closed
Beta waves are strongest
from frontal lobes; evoked
by visual stimuli and
mental activity
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EEG Waves continued
 Theta
waves come from
temporal and occipital lobes
 Common in newborns
 In adults indicates severe
emotional stress
 Delta waves are from cerebral
cortex
 Common during adult sleep
and in awake infants
 In awake adult indicates
brain damage
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Sleep
2
types of sleep are recognized
REM - rapid eye movement
EEGs are similar to awake ones
Type when dreaming occurs
Non-REM has delta waves
Appears to be crucial for consolidation of short- into
long-term memory
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Cerebral Lateralization
Refers
to specialization of each hemisphere for certain
functions
Each cerebral hemisphere controls movement on opposite
side of body
And receives sensory info from opposite side of body
Hemispheres communicate thru the corpus callosum (Fig
8.1) which contains about 200 million fibers
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Language
 Language
areas of brain are known mostly from aphasias
 = speech and language disorders due to brain damage
 Broca’s area is necessary for speech
 Wernicke’s area is involved in language comprehension
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Limbic System and Emotion
 The
hypothalamus and
limbic system (shown in
green) are crucial for
emotions
 Including aggression,
fear, feeding, sex and
goal-directed behaviors
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Memory
Includes
short- and long-term memory
Involves a number of regions in brain
There are two types of long-term memory
Non-declarative (explicit) includes memories of simple
skills and conditioning
Declarative (implicit) includes verbal memories
Amnesiacs have impaired declarative memory
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Memory continued
 Hippocampus
is critical
for acquiring new
memories
 And consolidating
short- into long-term
memory
 Amygdala is crucial for
fear memories
 Storage of memory is in
cerebral hemispheres
 Higher order processing
and planning occur in
prefrontal cortex
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Long-Term Potentiation (LTP)
Is
the increased
excitability of a
synapse after high
frequency
stimulation
Glutamate activates
AMPA and NMDA
postsynaptic
receptors in
hippocampus
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Neurogenesis in Hippocampus
Appears
to be crucial for learning and memory
Hippocampus contains neural stem cells that continually
produce new neurons (neurogenesis)
Stress or depression impede learning and cause
hippocampus to shrink
Stress reduction and antidepressants return size to normal
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Pituitary Gland
 Is
divided into anterior and
posterior lobes
 Posterior pituitary stores and
releases ADH (vasopressin) and
oxytocin
 Both made in hypothalamus
and transported to pituitary
 Hypothalamus produces
releasing and inhibiting
hormones that control anterior
pituitary hormones
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Hindbrain - Cerebellum
 2nd
largest structure in brain
 Receives input from proprioceptors (joint, tendon and muscle
receptors)
 Involved in coordinatng movements and motor learning
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Hindbrain - Medulla
 Contains
all tracts that
pass between brain and
spinal cord
 And many nuclei of
cranial nerves
 And several crucial
centers for breathing
and cardiovascular
systems
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Spinal Cord Tracts
Sensory
info from body travels to brain in ascending spinal
tracts
Motor activity from brains travels to body in descending
tracts
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Ascending Spinal Tracts
 Ascending
sensory
tracts decussate
(cross) so that brain
hemispheres receive
info from opposite
side of body
 Same for most
descending motor
tracts from brain
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Descending Spinal Tracts
 Are
divided into 2 major
groups:
 Pyramidal (or corticospinal)
tracts descend from cerebral
cortex to spinal cord without
synapsing
 Originate in motor cortex
 Function in control of fine
movements
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Descending Spinal Tracts continued
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Peripheral Nervous System (PNS)
Consists
of nerves that exit from CNS and spinal cord, and
their ganglia (= collection of cell bodies outside CNS)
Nerves (coming out of CNS)
Ganglia (neurons outside of CNS)
Sensors (eye=CNS)
ENS (enteric-neurons in the gut)
Supra-adrenals
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Spinal Nerves
continued
There
are 31
pairs:
8 cervical,
12 thoracic,
5 lumbar,
1 coccygeal
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Reflex Arc
 Is
a simple sensory input, motor output circuit involving only
peripheral nerves and spinal cord
 Sometimes arc has an association neuron between sensory and motor
neuron
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